U.S. patent number 8,947,977 [Application Number 05/504,958] was granted by the patent office on 2015-02-03 for fuzing arrangements.
The grantee listed for this patent is Brian Jackson, James Tomlinson. Invention is credited to Brian Jackson, James Tomlinson.
United States Patent |
8,947,977 |
Tomlinson , et al. |
February 3, 2015 |
Fuzing arrangements
Abstract
A proximity fuzing arrangement for fuzing warheads carried by
missiles which reduces the likelihood of the missile being
detonated prematurely by such cases as rain or enemy counter
measures. The fuzing arrangement includes at least two channels
responsive to target signals in different frequency bands and also
includes means for comparing the signals in these channels to
distinguish between spurious signals such as enemy counter measures
or rain and so called "true target signals".
Inventors: |
Tomlinson; James (Wells,
GB), Jackson; Brian (Wells, GB) |
Applicant: |
Name |
City |
State |
Country |
Type |
Tomlinson; James
Jackson; Brian |
Wells
Wells |
N/A
N/A |
GB
GB |
|
|
Family
ID: |
52395717 |
Appl.
No.: |
05/504,958 |
Filed: |
September 6, 1974 |
Foreign Application Priority Data
Current U.S.
Class: |
367/97; 102/427;
342/68 |
Current CPC
Class: |
F42C
13/02 (20130101) |
Current International
Class: |
F42C
13/02 (20060101) |
Field of
Search: |
;367/97 ;342/68
;102/427 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Pihulic; Daniel
Attorney, Agent or Firm: Crowell & Moring LLP
Claims
What we claim is:
1. A proximity fuzing arrangement comprising means for transmitting
radiation and receiving such radiation after reflection from echo
sources, means for processing the received radiation so as to
derive target signals indicative by their frequency of relative
motion between the transmitting and receiving means on the one hand
and the echo sources on the other hand, at least three signal
channels, each effective to pass target signals in a respective
frequency band, the signals S11 passed by a first of said channels
including true target signals and spurious signals, the signals S12
passed by a second of said channels encompassing substantially all
signals produced in response to rain, and the signals S13 passed by
a third of said channels including substantially only signals
produced in response to enemy counter measures, and means for
combining the signals passed by said channels to distinguish true
target signals from spurious signals, the means for combining being
adapted to form the combinations S11+S12-mS13 and S11+S13-mS12,
where m is a constant, in separate combining circuits and outputs a
signal, via suitable electronic components, to a trigger
arrangement when either of said combinations is of a predetermined
character.
2. A system according to claim 1 wherein one of said channels
responds to a frequency band which encompasses substantially all
target signals produced by rain and the said channel is coupled to
a gain control circuit preceding the said channels so as to permit
the signals to said channels to be reduced in the presence of
rain.
3. A system according to claim 1 wherein an offset signal, k, is
added to one or both of said signals S12 and S13, of such a value
as to give a required control of the rate at which false alarms are
generated by signal fluctuations.
4. A system according to claim 3 wherein said offset signal, k, is
arranged to be responsive to the level of said signals S12, so as
to be of such a value as to afford a required adjustment of the
threshold of response of the system to rain.
5. In a proximity fuzing arrangement for fuzing a warhead carried
by a missile, and including means for obtaining input signals
indicative by their frequency of relative speed between the missile
and a target but being susceptible to contamination by enemy
counter measures and natural precipitation, a circuit arrangement
for receiving said input signals and discriminating against said
contamination, the circuit arrangement comprising a first channel
adapted by filtering to pass substantially only signal components
included in said input signals indicative of contamination due to
enemy counter measures, a second channel adapted by filtering to
pass substantially only signal components included in said input
signals and indicative of contamination due to natural
precipitation and enemy counter measures, a third channel adapted
by filtering to pass signal components, included in said input
signals, and indicative of true target signals and/enemy counter
measures, and combining circuits connected to receive the signal
components passed by the three channels and to form weighted
combinations of said components, said combining circuits comprising
a first circuit for combining the signal components passed by all
three channels with discrimination against signal components passed
by said first channel, a second circuit for combining the signal
components passed by all three channels with discrimination against
signal components passed by said second channel, and gating means
for responding to an output signal, derived from either of said
first and second circuits and having a predetermined characteristic
and conveying such output signal to trigger circuit means included
in said fuzing arrangement.
6. An arrangement according to claim 5 wherein said first circuit
for combining is adapted to add together the signal components
passed by said second and third channels and to subtract from the
sum an integral multiple of the signal components passed by said
first channel, and wherein said second circuit for combining is
adapted to add together the signal components passed by said first
and third channels and to subtract from the sum an integral
multiple of the signal components passed by said second
channel.
7. An arrangement according to claim 6 wherein the two integral
multiplying factors are equal.
8. An arrangement according to claim 6 wherein both of said factors
equal four.
9. An arrangement according to claim 5 including automatic gain
control amplifier means connected to receive the signal components
passed by said second channel and to convey such components to a
common automatic gain control attenuator means in the path of said
input signals to each of said channels.
Description
The present invention relates to fuzing arrangements, and it
relates especially to proximity fuzing arrangements for fuzing
warheads carried by missiles.
It is known that proximity fuzes, i.e., fuzes which cause the
detonation of a warhead when it is at a predetermined distance away
from a target, the distance depending upon the conditions of
attack, are substantially more lethal than impact fuzes. It is
therefore of advantage to utilise proximity fuzes in missiles, but
such fuzes can be caused to trigger prematurely by external causes
such as enemy counter measures or naturally occurring phenomena
such as rain.
It is an object of this invention to provide a proximity fuzing
arrangement in which the abovementioned difficulties are
reduced.
According to the invention there is provided a proximity fuzing
arrangement comprising means for transmitting radiation and
receiving such radiation after reflection from echo sources, means
for processing the received radiation so as to derive target
signals indicative by their frequency of relative motion between
the transmitting and receiving means on the one hand and echo
sources on the other hand, a plurality greater than two of signal
channels, each responsive to target signals in differing respective
frequency bands, and means for comparing the signals of said
channels so as to permit the arrangement to distinguish true target
signals from spurious signals where the terms "true target signals"
and "spurious signals" as hereinafter described. Preferably one of
said channels responds to a frequency band which encompasses
substantially all target signals produced by rain and the said
channel is coupled to a gain control circuit preceding the said
channels so as to permit the signals fed to said channels to be
reduced in the presence of rain.
In order that the invention may be clearly understood and readily
carried into effect, one embodiment thereof will now be described,
by way of example only, with reference to the accompanying
drawings, of which: --
FIG. 1 shows in block diagrammatic form, part of a fuzing
arrangement in accordance with one example of the invention,
and
FIG. 2 shows a modification to that arrangement in accordance with
one example of the invention.
Referring now to FIG. 1, target signals indicative by their
frequency of the relative speed between a missile and one or more
echo sources are applied to a Doppler filter 1 which has a pass
band between 1 KHz and 100 KHz, which encompasses the useful band
of target signal frequencies and thus serves to reject noise
signals outside this band. The signals passed by filter 1 are fed
to an automatic gain control attenuator 2 and thence to an
amplifier 3 which is arranged to effect amplification by about 50
dB, with substantially constant effect over the whole spectrum of
frequencies passed via the filter 1.
Amplified target signals from the amplifier 3 are fed in parallel
to a bandpass filter 4, which has a pass band of 30 KHz to 70 KHz,
and to a notch filter 5 which has a stop band substantially centred
on the centre of pass band of filter 4, i.e. 50 KHz. The notch
filter 5 feeds, in parallel, a low bandpass filter 6 which has a
pass band from 1 KHz to 30 KHz and a high bandpass filter 7 which
has a pass band from 70 KHz to 100 KHz. Each of the filters 4, 6
and 7 feeds a respective one of three detector circuits 8, 9 and 10
and each detector circuit feeds a respective one of three 0.1
millisecond integrating circuits 11, 12 and 13.
The signals passed by filter 4 will contain rain and ECM signals,
which will be known as "spurious signals", and also "true target
signals" where "true target signals" are those received by
reflection from an intended enemy target.
Output signals S11, S12 and S13 each from respective integrators
11, 12 and 13 are applied in parallel to two comparing circuits 14
and 15; the two comparing circuits comprising summing and
differencing circuits and being effective to form the combinations:
S11+S12-4S13 and -4S12+S11+S13 respectively.
If either of circuits 14 or 15 produces a positive output signal
from its comparison of weighted positive and negative values, the
said output signal is passed via an `OR` gate 16 to the trigger
output terminal 17. The output signal is then processed to fire the
warhead in accordance with predetermined proximity conditions
consistent with the prevailing attack situation. Such processing is
known and will not be more fully described herein. In this example
a weighting factor of four is applied to noise signals S12, and S13
though any suitable weighting factor could be used.
It will be observed that, in view of the signal comparison which is
effected between target signals passed through the three signal
channels, the notch filter 5 is used to provide good signal
separation (i.e. lack of cross talk) between the various
channels.
By means of the comparisons, it is ensured that, in the presence of
a target signal, a subtraction of noise from signal plus noise is
carried out, in one or other of the circuits 14 or 15. Since ECM is
generally presented as broad band noise it appears, if present, on
all three signal channels, however, the required target signals are
substantially confined to the band of filter 4. The subtraction
process therefore provides the target signals substantially free of
ECM signals. A reduction in noise also occurs because of the
reduction in bandwidth of the signals in the various channels.
The present example of the invention includes a further refinement,
namely an automatic gain control signal which is derived from the
output of integrator 12 and is fed via an amplifier 18 to the
automatic gain control attenuator 2. This expedient permits the
sensitivity of the fuze arrangement to be reduced during rain, but
only to the extent necessary to prevent premature firing. It has
been found that the target signals derived in response to rain fall
substantially entirely within the frequency band of the filter 6.
Thus, in the presence of signals within the frequency band, the
gain of the arrangement is reduced by an amount dependent upon the
amplitude of such signals. This does not totally "blind" the
missile, even when the gain is reduced by a substantial amount,
since the signals to be compared in circuits 14 and 15 have all
been equally affected by the reduction in gain.
Previously it has been usual in fuzing arrangements to use an
automatic gain control signal derived from noise channels to
suppress the gain of the system in the presence of constant ECM in
a manner similar to that described above for rain. However, such
methods are vulnerable to switched ECM, when the ECM signals are
switched off the gain of such a system rises to its normal level
and if the ECM signals are then switched on again the automatic
gain control may not reduce the gain fast enough to prevent
triggering. The arrangement described above, however, involves
direct comparison and, not being subject to the delay of the
automatic gain control, is able to protect against switched ECM in
addition to constant ECM. Further protection against switched ECM
may be obtained by arranging that the reference channel integrators
12 and 13 have a short rise time and a longer fall time than the
other integrator.
A further modification to the invention is obtained if either or
both of the comparators 14 and 15 is replaced by a comparator as
shown in FIG. 2. A constant term k is added to one or both of the
noise channel signals S12 and S13 to form the combinations: --
S11+S12-4S13-k and S11+S13-4S12-k the comparator shown in FIG. 2 is
arranged to provide the second condition and is therefore a
replacement for comparator 15. The comparator then compares
positive and negative values and responds in the same manner as in
said comparator's un-modified design. Although k is shown as a
signal applied to a separate -1 input other arrangements may be
used to achieve the same effect. Adjustment of the factor k gives
control of the rate at which false alarms are generated by noise
signals present on the channel to which it is added. Thus, in the
arrangement of FIG. 2, k is added to the signal which would include
any noise due to rain. The factor k is then used to adjust the
threshold of response to rain. Means may be provided for k to be
responsive to the level of signal S12 such that the false alarm
rate remains constant in the presence of rain. In such a case it
may be possible to omit the amplifier 18 and automatic gain control
2. Similar arrangements may be made for the other channels.
The embodiment of the invention described hereinbefore is a
preferred embodiment, but it is not the only practical realisation
of the invention. For example, a straightforward approach is to use
three comparators, one for each channel, the outputs of which feed
a common `OR` gate. In this case, each comparator is balanced--i.e.
it has a positive and negative input. The positive input to each
comparator is the signal derived from its respective channel,
whereas the negative input in each case represents the sum of the
signals derived from the other two channels. In this way, each
comparator is based off by noise in the other two channels.
* * * * *